I want to create a summon ability. Like this:
1) costs energy
2) unit plays animation
3) at certain point in animation, summoned unit appears

What is a good dummy ability to base this on? I experimented with burrow, but ran into issues.
Step 3) is NOT the issue, I know how to do this with GPTP.

Rather than basing it on an ability at all, I'd recommend using the "Carrier Stop" or "Reaver Stop" orders. These are pretty useful for actions where you just want the player to press a button and have something happen.

Here's a skeleton of what that might look like:



You will need to make sure that you edit the requirements for the Carrier Stop order so that your unit can use it.

As far as playing an animation goes, you can use unit->sprite->playIscriptAnim() to do that, and the sigorder iscript opcode to communicate back to GPTP. So perhaps our code might look something like this:



And our iscript something along these lines:



to ensure that we summon the unit at the appropriate point in the animation.